Underdoped YBCO Research Articles

The effect of oxygen depletion on the in-plane resistivity and Hall coefficient of crystalline thin films of YBa 2(Cu 1−xZn x) 3O 7−δ

The different effects of in-plane or out-of-plane doping on the normal state transport properties of fully oxygenated YBCO are fairly well established. Little is known, however, about the effects of in-plane impurities on oxygen deficient or underdoped YBCO. To address this issue we report measurements of R H(T) and ϱ ab(T) of laser ablated crystalline thin films of YBa 2(Cu 1−xZn x) 3O 7−δ with 0 ≤ x ≤ 0.02 and 0 ≤ δ ≤ 0.28, and discuss our results in relation to recent specific heat measurements by Loram and co-workers.

Cross relaxation and the bilayer coupling in Y 2Ba 4Cu 7O 15

There is strong experimental evidence for substantial antiferromagnetic coupling between the CuO 2 planes of the bilayers in YBCO compounds. The acoustic mode of the spin excitation spectrum has been measured but the optic mode has not been observed. Theoretical estimates suggest values for the antiferromagnetic interplane coupling as large as 10 meV. It has been proposed that this coupling is responsible for the spin gap in the underdoped YBCO compounds. In the recently synthesized compounds Y 2Ba 4Cu 7O 15 with alternating single/double chain blocks, it is possible to distinguish between the CuO 2 planes in a bilayer. We propose a nuclear magnetic cross relaxation experiment to directly measure the strength of the coupling between the two planes of a bilayer. The temperature dependence and magnitude of this cross relaxation is predicted.

Copper spin-spin NMR relaxation in YBCO and a comparison between NMR and inelastic neutron scattering

The analysis of the 63Cu nuclear spin-spin relaxation rate [T 2 −1 ∝ χ′(QbdQ AF] data in the normal state of YBCO provides a missing link allowing us to construct a common picture for the NMR and the inelastic neutron scattering results. Nearly the same correlation length for antiferromagnetic fluctuations is found for both techniques. As these correlation lengths are very short, the description of the system should be revised. The relevant experimental data are presented for an optimal and slightly underdoped YBCO single crystals belonging to the “90 K phase”.